On Wed, Feb 01, 2023 at 04:17:33PM +0800, Yin Fengwei wrote:
> The shared fault handler can also benefit from fault-around. While it
> is uncommon to write to MAP_SHARED files, applications that do will see
> a huge benefit with will-it-scale:page_fault3 (shared file write fault)
> improving by 375%.
>
> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> mm/memory.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 7a04a1130ec1..51c04bb60724 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4546,6 +4546,17 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
> struct vm_area_struct *vma = vmf->vma;
> vm_fault_t ret, tmp;
>
> + /*
> + * Let's call ->map_pages() first and use ->fault() as fallback
> + * if page by the offset is not ready to be mapped (cold cache or
> + * something).
> + */
> + if (should_fault_around(vmf)) {
> + ret = do_fault_around(vmf);
> + if (ret)
> + return ret;
> + }
> +
I believe it bypasses ->page_mkwrite() completely, no?
So you get a writable PTEs without notifying the filesystem. Smells like a
data loss.
> ret = __do_fault(vmf);
> if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
> return ret;
> --
> 2.30.2
>
>
--
Kiryl Shutsemau / Kirill A. Shutemov
